In general, a housing of an electronic device is formed of a plurality of metal plates for simplifying assembling and maintenance thereof. On the other hand, the electronic device must be electromagnetically shielded to cause no adverse effects on peripheral devices due to electromagnetic waves generated from the electronic device and also not to allow malfunction of the electronic device due to any external electromagnetic waves. Therefore, in view of preventing leak and entry of an electromagnetic wave from the joining portion of metal plates forming the housing, an electromagnetic wave shielding structure is required at the relevant joining portion.
As an example of the electromagnetic shielding structure at the joining portion, the JP-A No. 2001-284875 and the registered Japanese Utility Model No. 3065107 disclose a structure in which a plurality of tongue pieces having the spring property are provided to metal plates and the metal plates are bonded through these tongue pieces as the conductive part.
The electromagnetic shielding structure of the background art will be explained with reference to FIG. 6 to FIG. 9. FIGS. 6 and 7 are de-assembled perspective views of the housing including the electromagnetic shielding structure of the background art. In FIGS. 6 and 7, the housing 500 is formed by assembling a ceiling plate 50 closing an aperture to the housing body 40 of the housing having the almost U-shape cross-section having an aperture at the upper part. At the circumference part of the aperture of the housing body 40, belt type flat portions 41 are formed to receive the ceiling plate 50. These belt type flat portions 41 are provided with a plurality of plate springs 44 where the relevant belt type flat part 41 is cut and erected along the longitudinal direction of the relevant belt type flat portions 41. The housing body 40 and the ceiling plate 50 are bonded with each other via a plurality of plate springs 44. With the structure as explained above, the housing body 40 and the ceiling plate 50 are conductive via a plurality of plate springs 44 and thereby leak and entry of the electromagnetic wave are prevented at the joining portion. Here, direction of each plate spring 44 becomes parallel for the longitudinal direction of the belt type flat portions 41 in FIG. 6 and also becomes vertical for the longitudinal direction of the belt type flat portions 41 in FIG. 7. FIGS. 8 and 9 illustrate respectively a part D1 in FIG. 6 and a partially enlarged diagram of a part D2 in FIG. 7. As illustrated in FIG. 8 and FIG. 9, in the electromagnetic shielding structure of the background art, each plate spring 44 is provided in any of the parallel direction or vertical direction for the longitudinal direction of the belt type flat portion 41.
Following requirements are generated for such electromagnetic shielding structure.
In recent years, with improvement in the operation rate of a computer, the frequency of the electromagnetic wave generated by an electronic device is increasing. Here, in view of shielding the electromagnetic wave of higher frequency, an interval between the contact points of the plate spring 44 and ceiling plate 50 (size c1 in FIG. 8 and size c2 in FIG. 9) must be further shortened. Accordingly, request for shortening the intervals (hereinafter referred to as contact interval c1, c2 between the plate spring 44 and ceiling plate 50 is also increasing.
Moreover, the plate spring itself is requested to have higher elasticity in order to improve the shielding performance by surely making conductive the housing body 40 and ceiling plate 50. In order to attain elasticity of the plate spring itself, length of the plate spring itself (size b1 in FIG. 8 and size b2 in FIG. 9) must be further elongated. Namely, it is also requested to make longer the length of the plate spring itself (hereinafter, referred to as plate spring length) b1, b2.
Moreover, it is also requested to make smaller the area of the joining portion between the housing body 40 and ceiling plate 50, namely to make narrower the width of belt type flat portion 14 (size a1, in FIG. 8 and size a2 in FIG. 9) in order to realize cost reduction and size reduction of the housing 500.
As explained above, three requirements are issued for the electromagnetic shielding structure. However, these three requirements are not simultaneously satisfied in the electromagnetic shielding structure of the background art. In more practical, when the plate spring length b1 is elongated in order to enhance elasticity of the plate spring 44 in the electromagnetic shielding structure of FIG. 8, the contact interval c1 must also be elongated, resulting in lowering of the shielding performance for the high frequency electromagnetic wave. The reasons are that it is impossible to make the contact interval c1 equal to or shorter than the plate spring length b1 and if only the plate spring length b1 is elongated without elongation of the contact interval c1, strength of the housing 500 is remarkably lowered. Moreover, when the plate spring length b2 is elongated to enhance elasticity of the plate spring 44 in the electromagnetic shielding structure of FIG. 9, the width a2 of the belt type flat portion 41 must also be elongated, resulting in increase in size and cost of the housing 500.
Requirements for structures illustrated in FIG. 6 to FIG. 9 have been explained from the viewpoint of the electromagnetic shielding function, but the following requirements are also generated when the structures illustrated in FIGS. 6 to 9 are considered as the joining structure.
First, it is desirable for improvement in close contact between the housing body 40 and ceiling plate 50 to make dense distribution of a plurality of plate springs 44 for the longitudinal direction of the belt type flat portion 41. Namely, requirement for making shorter the contact intervals c1, c2 is also generated in FIG. 8 and FIG. 9.
Moreover, the plate spring 44 itself should desirably have higher elasticity in order to improvement in the close contact. Namely, it is also required to make longer the plate spring length b1, b2 in FIG. 8 and FIG. 9.
Moreover, in order to realize reduction of cost of the housing 500, a request for reducing the area of the joining portion of the housing body 40 and ceiling plate 50, namely a request for making narrower the width (size a1 in FIG. 8 and size a2 in FIG. 9) of the belt type flat portion 41 is issued.
As explained above, three requirements are generated for the contact structures illustrated in FIG. 6 to FIG. 9. However in the joining structure of the background art, these requirements cannot be satisfied simultaneously. In more practical, when plate spring length b1 is elongated in order to enhance elasticity of the plate spring 44 in FIG. 8, the contact interval c1 must also be elongated, resulting in the result that distribution of a plurality of plate springs 44 becomes coarse. Moreover, in FIG. 9, when the plate spring length b2 is elongated in order to enhance elasticity of the plate spring 44, the width a2 of the belt type flat portion 41 must also be elongated, resulting in rise of cost or the like.